Method and apparatus for determining hydrocarbon content of solid earth formation samples



July 16, 1957 R. w. ROCHON 4 METHOD AND APPARATUS FOR DETERMINING HYDROCARBON CONTENT OF SOLID EARTH-FORMATION SAMPLES Filed Nov. 1'7, 1954 I 'V V EN TOR.

Robe/f W Roe/200 NBY EXTRACT/0N:

,4 rTOR/VE Y United States Patent C METHOD AND APPARATUS FOR DETERMINHJG HYDROCARRON CONTENT OF SOLKD EARTH FORMATIGN SAWLES Robert W. Rochon, San Antonio, Tex, assignor to Manarch- Logging Company, Inc, San Antonio, Tern, a corporation of Texas Application-November 17, 1954, Serial No. 469,361

7 Claims. (Cl. 23-230) This invention relates to the determination of the hydrocarbon gas content of earth samples. More particularly, the present invention is directed to a method and apparatus for measuring the hydrocarbon gas content of solid cores removed from earth formations during the drilling of a well, such as an oil or gas well.

This application is a continuation-in-part of my copending applications Serial No. 381,223, filed September 21, 1953, now U. S. Patent Number 2,749,220, and Serial No. 437,436, fiied June 17, 1954.

The present invention is directed to improvements in the methods and apparatus described in the aforementioned applications, by which it becomes possible to evaluate the production characteristics of earth formations.

Mere. determination of the presence and quantity of hydrocarbons in a particular earth sample ordinarily is notsufiicient to apprise the well operator of the producing characteristics of the formation. One of the principal difficulties encountered in logging wells is to distinguish between earth formations which will produce oil and those which contain residual oil but produce water; that is, both such reservoirs will, by conventional tests, indicate the presence of liquid hydrocarbon, but to determine their producing characteristics, other and more elaborate tests are required which are, at best, very inconclusive. One of the important factors in rendering an earth formation producible of its contained liquids is the presence of relatively low boiling but normally liquid hydrocarbons which are readily volatilizable upon reduction in pressure in order to provide energy from the volatilizing or evaporation of the lighter components for lifting the fluid to the surface. It is relatively difficult by conventional core analysis methods to determine the volatility characteristics of the contained hydrocarbons.

In accordance with the present invention a method and apparatus is provided whereby a small core, such as a conventional side-hole core, may be examined quickly and by a simple procedure to determine the presence of hydrocarbons and to, at the same time, determine volatility characteristics of the hydrocarbons. By means of the present method conditions simulating the normal depletion process itself are produced and the information derivable therefrom will provide the operator with important and valuable information as to the producing characteristics of the earth formation being examined.

In accordance with the present invention, a core sample is subjected to a series of vacuum extractions, the core sample being maintained under reduced pressure for a period of time following each extraction in order to permit further volatilization of liquid hydrocarbons which may be contained in the sample. The relative volumes of gas extracted in the successive extractions will provide an indication of the character of the hydrocarbons inthe sample, and will also serve to distinguish between relatively non-volatile residual oil and the so-called live oil; that is, oil containing volatile hydrocarbons which, when. the'pressure is reduced, as will occur in normal "ice operations, will provide theenergy to cause the oil to flow from the formation into the well.

Another object is to provide an apparatus suitable for performing the method of this invention.

Other and more specific objects and advantages of this invention will become more readily apparent from the following detailed description when read in conjunction with the accompanying drawing which illustrates a form of apparatus useful in connection with the present invention.

In the drawing, Figs. 1 to. 5 illustrate a form of apparatus in accordance with the present invention, the several figures illustrating a series of stages in the manipulation of the apparatus in performing a method for determining the gas content of solid earth samples; and

Fig. 6 is a graph constructed from information derived by means of the invention, and illustrative of the relative volatility characteristicsof the hydrocarbons present in a plurality of earth samples.

Referring to the drawing, the apparatus includes a hollow-vessel 10 which is preferably cylindrical but may be of other suitable shape, and which may be constructed of glass or rigid plastic and adapted to contain a body of liquid mercury 11. Vessel 10 has at its upper end an elongated neck 12, which may be formed integrally with the vessel and which is in open communication with the interior of the vessel. The lower end of vessel It is provided with a connection 13 to which is attached one end of a flexible tube 14. The other end of the flexible tube is connected to a generally conventional levelling bulb 15 which serves as a reservoir for the mercury. It will be understood that by raising and lowering levelling bulb 15 relative to vessel 10, the level of mercury in the latter may be correspondingly raised and lowered. The upper end of neck 12 communicates with a narrow tube 16 which is, in turn, connected to a multi-port valve 17, such as a conventional three-way valve which, by appropriate manipulation, may be employed to close tube 16 or to place the latter selectively in communication with either a pipe 18 or a pipe 19. Pipe 18 leads to a hydrocarbon gas analyzer 20, preferably of the wellknown hot filament type. The details of such analyzer do not form a part of the present invention but, as is well understood, such instruments employ a Wheatstone bridge arrangement in one leg of which is mounted a heated platinum filament which, when exposed to the hydrocarbon gas-air mixture, becomes more highly heated and unbalances the bridge. The degree of unbalance to produced is a measure of hydrocarbon gas content of the air-gas mixture, and is indicated or recorded on a suitable meter, such as the meter 21, which may be calibrated to indicate or record directly the percentage of hydrocarbon gas in the mixture.

Pipe 19 extends through a stopper 22, constructed of rubber or similar flexible resilient material, and the stopper is adapted to be removably inserted in the open end of a small container 23 (Fig. 2), which is adapted to contain a sample 24 which may be a sidehole core or drill cuttings. The pipe 19 communicates through stopper 22 with the interior of container 23. A two-way stop cock 25 is interposed in pipe 19 between three-way valve 17 and container 23 whereby to control communication through pipe 19.

Neck 12 is provided with an appropriately positioned longitudinal scale 26 which may be marked directly on the exterior of the neck or may be a separate scale suitably positioned alongside the neck. The scale is provided with graduations calibrated to provide a measure of the internal volume of the neck above any point therein, for purposes to be more fully described hereinafter.

The described apparatus is operated in, the following position illustrated in Fig. l. -tainer has been properly connected, the mercury level will manner: Before sample container 23, having the sample 24 therein, is attached to the apparatus and while the pipe 19 is open to the atmosphere, as illustrated in Fig. 1, levelling bulb will be raised to a height sufficient to completely fill the apparatus with mercury to the level of pipe 19, whereby to displace all extraneous air from the interior of vessel 10, neck 12 and tube 16. In this operation, valve 17 will be turned so as to place tube 16 in communication with pipe 19 and stopcock 25 will be in the position shown in Fig. l in order that the displaced air may be discharged to the atmosphere.

The sample 24 will then be placed in container 23 which will be attached tightly to stopper 22, as illustrated -in Fig. 2, it being understood, however, that at this moment the apparatus will be filled with mercury to the When the sample conbe lowered by lowering levelling bulb 15, as illustrated in Fig. 2, to drop the mercury level in vessel 19 to a position approximately level with the bottom of vessel 10. Lowering of the mercury level with valve 17 and stop cock 25 positioned as shown in Fig. 2 to provide communication between sample container 23 and vessel It) will evacuate sample container 23 and thereby cause any gas contained in sample 24 to be sucked out of the sample, and together with the air in container 23 drawn into vessel 10.

By making the overall volume of vessel 10 and neck 12 sufficiently great with respect to the volume of sample container 23, the extent to which the sample may be evacuated can be effectively regulated. For example, if container 23 with stopper 22 inserted therein, has an internal volume of cc., vessel 10 and neck 12 may be made to have an overall internal volume of 250 cc., or approximately twelve and one-half times the volume of container 23. If it is assumed that sample 24- will occupy one-half the volume of container 23 or 10 cc., it will be seen that the volume of vessel 10 and neck 12 will be approximately twenty-five times the unoccupied volume in container 23. Accordingly, when the mercury level is lowered to the bottom of vessel 10, it will be seen that the gas in the sample will expand about times its volume so that approximately 96% of any gas in the sample 24 will be evacuated therefrom and vessel 10 will contain about 96% of the expanded air-gas mixture. Thus the relative volumes of vessel 11) and container 23 may be employed to determine the degree of evacuation of the sample by appropriate reduction in the mercury level. Ordinarily the volume of vessel 10 and neck 12 will be made from 10 to times that of container 23. Neck portion 12 will preferably be made to have an internal volume about 10 to 20% of the total combined volume of vessel 10 and neck 12.

When the sample has been evacuated, as described, and the mixture of gas and air expanded and drawn into vessel 10, valve 17 is moved to the position illustrated in Fig. 3 to close-oil communication between vessel 10 and pipes 18 and 19, thereby sealing vessel 10. At the same time stop cock 25 will be turned to the closed position, as shown in Fig. 3, in order to maintain sample 24 under the reduced pressure which had been applied to container 23 as described, to thereby accomplish an important feature of the invention as will be subsequently described. With valve 17 and stop cock 25 closed, the level of mercury is then raised to displace the gas-air mixture from vessel 10 into neck 12 in order that its volume may be measured by means of scale 26. Valve 17 will now be turned to a position placing tube 13 in communication with tube 16 and neck 12, as shown in Fig. 4. The levelling bulb is lowered and external air will be drawn through analyzer 2 3 and pipe 13 into neck 12 by reason of the reduced pressure produced therein by lowering the mercury level to a position, as illustrated in Fig. 4, until the pressure is equalized with the atmosphere and the larger measured volume of resulting air-gas mixture in neck 12 will then be at atmospheric pressure. The extraneous air which entered neck 12 will serve to dilute the gas in the mixture to a gas-air ratio which will be below the lower explosive limit, a condition which is requisite for etficient functioning of hot filament detectors of the kind described above.

As soon as the air-gas mixture in neck 12 has attained atmospheric pressure, valve 17 is turned to the position illustrated in Fig. 5 wherein neck 12 and tube 16 are placed in communication with pipe 18 and gas analyzer 2a. Thereupon, levelling bulb 15 is raised to raise the mercury level in vessel 19 so as to displace the air-gas mixture from neck 12 through the analyzer which will indicate or record the percentage of gas in the air-gas mixture. Since the total volume is known, a simple computatic-n will provide the total quantity of gas in the mixture and hence the volume of gas originally present in sample 24.

By means of the above-described apparatus, it will be. seen that the quantity of hydrocarbon gas present in small earth samples, such as side-hole cores or drill cuttings, may be quickly and easily determined.

In addition to measuring the normally gaseous hydrocarbons which may be present in the earth samples, lower boiling hydrocarbons, such as pentanes, hexanes, heptanes, etc.,- will be volatilized by reduction in pressure in the sample container and these latter hydrocarbons may provide an indication or index of the presence of heavier liquid hydrocarbons in the related earth formations.

During the time interval required to complete the analysis of a gas sample following the closing of stop cock 25, sample 24 will have remained under the reduced pressure trapped in container 23 by the closing of stop cock 25. lt is found that if the liquid hydrocarbons which may be present in the sample contain relatively volatile components, such as propane, butane, pentane and hexane, the latter will, by virtue of the reduced pressure in container 23, undergo vaporization in proportion to the quantities present and their partial pressures, and the vaporized hydrocarbons may then be withdrawn and the volume determined by the repetition of the procedure previously described. The appearance of substantial additional volumes of gaseous hydrocarbons in a plurality of subsequent extractions of the same sample provides an important indication that the hydrocarbons in place are producible and will flow from the earth formation under normal producing conditions.

On the other hand, if the hydrocarbons originally present in the earth sample are largely normally gaseous, the great bulk will be withdrawn on the very first extraction and subsequent extractions will show very little additional gas. Similarly, if the hydrocarbons present in the sample are relatively high boiling, namely, dead oil, very little gaseous hydrocarbons will be obtained by the extraction.

By providing stop cook 25 and closing it after each extraction, and by making each extraction under substantially the same reduction in pressure, the data from two or more samples can 'be made reasonably comparable. The time interval between extractions will normally also be kept uniform to additionally assure uniform testing conditions. Ordinarily eight to ten separate extractions will be sufficient to provide the desired data for most samples but it will be obvious that the number of extractions, the time intervals allowed, the pressure reductions, etc., may be varied within rather wide limits.

Fig. 6 is a chart made from the data obtained by making a plurality of extractions in the manner described on three samples taken from slightly varying levels in a single four-foot earth section, all the samples indicating,

being examined. It will be seen that the volume percent of gas extracted by the first extraction is substantially the same for each sample. Hence, if only one extraction were performed, the several portions of the earth section would have appeared to have the same producing characteristics.

It will be noted, however, that in the case of graph A, the second and third extractions produced progressively increasing relatively large volumes of gas, the subsequent extractions producing substantial but progressively decreasing quantities of gas. This constitutes a very clear indication that the hydrocarbons contained in the upper portion of the earth section comprised live oil containing substantial quantities of light components which would provide the energy to enable that portion of the section to produce oil in what is most likely to be commercial quantities.

Graph B shows only a slight increase in gas volume on the second extraction and substantially constant amounts on subsequent extractions.

Graph C, the volumes of gas on all extractions are substantially uniform.

Graphs B and C, therefore, clearly show that the corresponding portions of the earth formation containlittle or no producible hydrocarbons.

From the foregoing, it will be seen that the method and apparatus according to the present invention provides relatively simple and efficient means for obtaining highly useful information as to character of oil and gas containing earth formations. It will be understood that changes and alterations may be made in the details of the illustrative embodiments within the scope of the appended claims but without departing from the spirit of this invention.

What I claim and desire to secure by Letters Patent is:

1. The method of determining the producible hydrocarbon content of earth formations, comprising, subjecting a sample of an earth formation while confined within a chamber to a plurality of successive vacuum extractions at substantially constant sub-atmospheric pressure, the sample being continuously maintained under said sub-atmospheric pressure for substantially uniform time intervals during each extraction, withdrawing the gaseous hydrocarbons extracted from the sample from the chamber after each extraction, and determining the volume of gaseous hydrocarbons Withdrawn from the sample in each extraction.

2. The method of determining the producible hydrocarbon content of earth formations, comprising, subjecting a sample of an earth formation while confined within a chamber to a plurality of successive vacuum extractions at substantially constant sub-atmospheric pressure, the sample being continuously maintained under said subatmospheric pressure for substantially uniform time intervals during each extraction, withdrawing the gaseous hydrocarbons extracted from the sample from said chamber after each extraction, determining the volume of gaseous hydrocarbons withdrawn from the sample in each extraction, and plotting the percentages of said extracted hydrocarbons by volume of said sample obtained in the several extractions against the number of said extractions to thereby obtain an indication of the producible hydrocarbon content of said earth formation.

3. The method of determining the producible hydrocarbon content of earth formations, comprising, subjecting a sample of an earth formation while confined within a chamber to a plurality of successive vacuum extractions at substantially constant sub-atmospheric pressure, the sample being continuously maintained under said subatmospheric pressure for intervals of about one minute during each extraction, withdrawing the gaseous hydrocarbons extracted from the sample from said chamber after each extraction, and determining the volume of gaseous hydrocarbons withdrawn from the sample in each extraction.

lit)

4. The method of determining the producible hydrocarbon content of earth formations, comprising, subject ing a sample of an earth formation while confined within a chamber to a plurality of successive vacuum extractions at substantially constant sub-atmospheric pressure, the sample being continuously maintained under said subatmospheric pressure for substantially uniform time in tervals during each extraction, withdrawing the gaseous hydrocarbons extracted from the sample from the chamber after each extraction, mixing the withdrawn hydrocarbons from each extraction with air to form an air-gas mixture of known volume, and determining the proportion of hydrocarbon gas in each said mixture.

5. The method of determining the producible hydrocarbon content of earth formations, comprising, subjecting a sample of an earth formation while confined within a chamber to a plurality of successive vacuum extractions at substantially constant sub-atmospheric pressure, the sample being continuously maintained under said subatmospheric pressure for intervals of about one minute during each extraction, withdrawing the gaseous hydrocarbons extracted from the sample from said chamber after each extraction, mixing the withdrawn hydrocarbons from each extraction with air to form an air-gas mixture of known volume, and determining the proportion of hydrocarbon gas in each said mixture.

6. The method of determining the producible hydrocarbon content of earth formations, comprising, subjecting a sample of an earth formation while confined within a chamber to a plurality of successive vacuum extractions at substantially constant sub-atmospheric pressure, the sample being continuously maintained under said subatmospheric pressure for intervals of about one minute during each extraction, withdrawing the gaseous hydrocarbons extracted from the sample from said chamber 'after each extraction, mixing the withdrawn hydrocarbons from each extraction with air to form an air-gas mixture of known volume, determining the volume of gaseous hydrocarbons withdrawn from the sample in each extraction, and plotting the percentages of said extracted hydrocarbons by volume of said sample obtained in the several extractions against the number of said extractions to thereby obtain an indication of the producible hydrocarbon content of said earth formation.

7. Apparatus for measuring hydrocarbon gas in earth samples, comprising, a hollow vessel having an elongated neck portion at its upper end and adapted to contain a body of liquid mercury, a mercury levelling bulb connected to the bottom of said vessel operable to controllably evacuate said vessel by raising and lowering the mercury level therein, a container adapted to receive an earth sample, a hydrocarbon gas analyzer, conduit means connecting said container and said analyzer to said vessel, a multi-port valve means interposed in said conduit means operable to selectively connect said vessel respectively with the interior of said container and with said analyzer, and a second valve means interposed in said conduit means between said multi-port valve means and said container to control communication with said container independently of the position of said multi-port valve means.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Serial No. 249,384, Weber (A. P. 0), published April 27, 1943. 

1. THE METHOD OF DETERMINING THE PRODUCIBLE HYDROCARBON CONTENT OF EARTH FORMATIONS, COMPRISING, SUBJECTING A SAMPLE OF AN EARTH FORMATION WHILE CONFINED WITHIN A CHAMBER TO A PLURATILY OF SUCCESSIVE VACUUM EXTRACTIONS AT SUBSTANTIALLY CONSTANT SUB-ATMOSPHERIC PRESSURE, THE SAMPLE BEING CONTINUOUSLY MAINTAINED UNDER SAID SUB-ATMOSPHERIC PRESSURE FOR SUBSTANTIALLY UNIFORM TIME INTERVALS DURING EACH EXTRACTION, WITHDRAWING THE GASEOUS HYDROCARBONS EXTRACTED FROM THE SAMPLEFROM THE CHAMBER AFTER EACH EXTRACTION, AND DETERMINING THE VOLUME OF GASEOUS HYDROCARBONS WITHDRAWN FROM THE SAMPLE IN EACH EXTRACTION. 